Cardiac arrhythmias are a widespread medical condition facing physicians today. Their most frequent cause is an abnormal routing of electricity though the cardiac tissue. While several surgical approaches have been developed for the purpose of treating or preventing different types of cardiac arrhythmias, ablation is now widely used as the preferred treatment. Typically, a physician places an endocardial catheter with an electrode at its tip inside the heart at a location where cells are giving off abnormal electrical signals. The electrode is activated according to various known modes of operation such that the adjacent targeted tissue is ablated and rendered non-conductive, halting the spread of improper cardiac signals.
The arrhythmia substrate is often deep in the wall of the heart, or transmural. Thus, the clinician performing the ablation wants the input energy and resulting heat to propagate entirely through the endocardium to the epicardium, thus thoroughly lesioning the substrate in question. However, critical structures lie directly outside the epicardium, and the fundamental conflict is one of depositing energy deep within the heart tissue on the one hand, but not damaging tissues, organs and structures beyond the heart wall, on the other. As an example, on average the esophagus in only 2 mm from the atrial epicardium yet the atrial is 3 mm thick. Therefore, ablationists essentially want to burn deep enough, but not too deep.
Although simple ablations are performed with relatively few complications, some of the more complex ablations that have been developed recently use more energy over longer periods of time. For example, whereas the standard ablation for atrioventricular nodal reentry requires only 60 seconds of burning, a standard ablation for atrial fibrillation (AF) may require 4000 seconds of burning. Furthermore, whereas traditional ablations are often done on the inner walls of the heart, the more complex ablations are often performed on the heart's free wall, which is even closer to the lungs, phrenic nerve, and esophagus. Recent case reports have shown complications and even death from burns that damage these structures after an AF ablation.
Modern radiofrequency ablation catheter procedures operate by delivering current between a small (2-8 mm) anode located in the tip of a standard ablation catheter coupled to a large surface area conductive cathode provided on the patient's back. Current flowing between the anode and the cathode is at its highest density at the tissue location directly adjacent to the treatment electrode. Thus, a planar sheet of the current flow can be modeled as a triangle with its apex at the ablation tip (anode) and its base on the patient's back (cathode). Though most of the burning is close to the apex of the triangle, the esophagus, lungs, and phrenic nerve are within the current density triangle. The current does not drop off sufficiently between the epicardium and the adjacent structures due to the inherent proximity.
There is therefore a need in the art for an effective electrode catheter that could be electrically coupled to an endocardial or other type of ablation catheter to provide better and safer modes of treatment. Particular needs remain for such a device with appropriate length, diameter, stabilization, steering capacity, and irrigation to allow effective energy transfers transmurally through the endocardial wall.
To overcome these limitations, we have conceived the subject device and method of use, as described in the Summary of the Invention and Detailed Description of the Drawings below.